Apparatus for coating indirectly heated cathodes



Dec- 11, 1951 A. lw. W. GAsT r-:TAL

APPARATUS FOR COATING INDIRECTLY HEATED CATHODES Filed Aug. 9, 1947 @SET IN VEN TORS w NN Patented Dec. Il, 1951 UNITE-D .STATE s PATENT ortica S- FOR COATING INDIRECTLY HETED CATHODES Application August .9, 1947, -S'eral No. 567,680 In Great Britain March 6, 19412 section i, :Public Law ccc, .August s, .1.946

' i Patent expires March 6, A1962 8 Claims. (Cl. 91u53) This invention relates to electric discharge devices, more especially thermionic valves, having indirectly-.heated cathodes and to the manufacture of the cathodes of such devices.

Indirectly heated cathodes usually comprise a ,metal cylinder coated with activating material.. In their manufacture, the activating material, or more often material from which the true ac tivating `material is produced by heat, is usually..deposited on the cylinder by spraying. dipping or .like process. .In .modern .thermionic valves having Yindirectly .heated cathodes, the clearance between the cathode and 4a neighborining electrode may be so small that variati-ons in' the thickness of the coatingthat are diiiicult to avoid in such processes may lead to kundesirable variations in `the characteristic of the resulting valve. Thus the tolerance onlthe diameter of the coated cathodemay be as .small as .D05 mm. The object of the invention is to provide a method of making activated indirectly heated cathodes in which the variation .in the diameter of the cathode is less than is easily at tained by merely spraying or dipping a cylinder :of iixed dimensions.

According to the invention, the manufacture of an activated indirectly heated cathode comprises the steps (l) forming on the outer surf face of a metal cylinder, whose diameter is less than that of the final cathode, a coating of activating material., or material from which acftivatng material is subsequently produced', so thick that the diameter of the coated cylinder -is .greater than that of the final cathode, (v2.) passiing the product of step 1) through a die in such a manner that the diameter of the coated cylnder is reduced by the removal of lpart but not vall of the said material.

one Yon each side vor the die, rise from the 'base plate; on each pillar slides a long sleeve, 'spring blessed away from the base plate. A cross bar, carried on the two sleeves, has on its low'er side a pin, directed ltowards the centre of 'the die. This pin is adapted 'to rit closely inside the metal cyl'- inder of a cathode.

'fin operation, r the cylinder of a cathode, a1- ready subjected to 'step 1), is slipped rover the pin. "The cross bar is then depressed against the springfbias. The cathode, centred rby the pin, is thus forced into the 'die and step `(2) is there` .fore performed.

` In a modiiicaton, ythe instrument 'just described s inverted, so that the cathode appreaches the die from below., 'instead of from above. 'Then the material removed by the die 'falls away from it, and does 'not tend to clog the die.

However this is not the preferred method. In the preferred method apparatus is used compri'sf ing a pair of coaxial pins, each fitting within the coated cylinder, each constrained so as to be translatable only along their common axis, one of the said rplus being spring-biassed so as to protrudey through the die.; and comprising also means for causing the other of the said `pinsto move towards the first-'mentioned pln through a predetermined distance.

One embodiment of the invention will now be described by way of example with reference'to 'the accompanying drawing wherein: Y

Figure 1 isa plan view of the apparatus of' the invention;- f

`liguret is an elevation partly in section along` the line 2--2"of Figure l;

' Figures 43 and d are plan views in' section of details showing the bases for the. pins of the. ap paratus;

o is a detail View in section of the die which may be used in the apparatus;

'. Figure 6 .shows a section'alize'd view of the lfric tion device for lcontrolling the speed of return motion ciY the apparatus.

Mln/the :drawinarests l and 2 are mounted on the common base 3, providing guides for the slidesd, 5 respectively. Slides 4, 5 carry respec tively at the ends turned towards each other a pin .f6 and a coaxial pin l. Both these pins pro;-

,tiect `from dat bases; the .base `of pin. l vis-shown clearly in Figure 3 at ia, the base 6a of pin 6 shown in Figure 4 abuts against the back face of slide 4. Slide i is pressed towards slide 5 by the spring 8, but is stopped by the die 9 through the hole in which pin 6 projects. Slide 5 is moved to and fro by the crank I!) operated by the wheel I I with handle I2. At the base of each pin is an annular ldepression I3 vand I4 in the slider, 1n which the end o'f the cathode locates itself. The wheel I I is provided with a friction device shown best in Figure 6 which prevents a too rapid return motion of the wheel, which might lead to scoring of the cathode. This device consists of a fibre plug I5 pressed against a face of the wheel by a spring I5 compressed by an adjustable screw Il.

In the embodiment shown the wheel makes a complete revolution during the treatment of a single cathode, so that the travel of the slide 5,

and therefore the length of that part of the cathode which passes through the die, is controlled by the throw of the crank; the machine is therefore adapted to deal with cathodes of one particular size only. But in modications adjustments are provided which enable cathodes of vdilerent length to be treated by the same machine. Thus a stop may be provided to prevent a complete revolution of the wheel; or the crank pin I6 may be adjustable along a radius of the wheel so that the throw for a complete revolution can be varied.

v In one mode of operating such apparatus described by way of example; one end of the coated cathode to be subjected to step (2) is slipped over the end of pin 6 that is protruding from the die. Pin I is then caused to approach pin 6 until its forward end enters the'other end'of the cathode. On continued approach of pin 1, this other end ofthe cathode abuts against a' base from which pin 'I -protrudes, so that the cathode is driven -further'over pin 6 until the first said end abuts against a base `from which pin 6 protrudes. During this stage part of the cathode passes throughthe die. When both ends of the cathode abut against the said bases, the cathode is pushed further through the die against the spring biassing 6, until the required part of the cathode has been scraped. Pin 1 is then withdrawn; the spring causes the cathode to follow it so far that the cathode can easily be removed from the die.

It will be realised that many minor variants of this procedure are possible. Thus one end of the cathode might be first itted over pin 'I and the other end fitted over pin 6 only as pin 'I moves forward.

If the cathode to be coated is 1.00 mm. in internal diameter with a wall 0.07 mm. thick, the pins 6, 'I may be conveniently 0.98 mm. in diameter and the diameter of the hole in the die 1.32 mm. The thickness of the coating left on the cathode after passage through the die will thenbe 0.09 mm. If the length of the cathode is 26 mm., the throw of the crank may be some 32.5 mm., the excess being allowed in order to permit of the cathodes being easily placed on the pins. The end of the cathode placed over the pin A will necessarily be scraped up to its eX- tremity; the vother end can be scraped very nearly to its extremity by adjusting .the position oftherest I in relation to the throw of the crank so that the base of the pin- I approaches very near to the die at one end ofv its travel. The part in the depression I4 cannot be scraped; but that -usuallyiibe ofno consequence, 'because a 57.5% BaCO3+43.5% SrCO3 (by weight) gm 3000 Necoloidine (5% solution in butyl acetate) ml-- 166 Anhydrous butyl acetate do-.. 1036 Methyl alcohol do-- 1800 Ethyl oXalate do-- 240 the mixture having been balled-milled for 16 hours. The dried layer should be of such a thickness, inthe example given above, that the external diameter of the cathode at the end of step (l) is some 1.35 mm.

What we claim is:

1. Apparatus for removing a portion of the electron emitting coating from the sleeve of a cathode having open ends, comprising a die having an opening therein of predetermined size, and means for causing said cathode to pass longitudinally through said opening in said die, said means including two coaxially disposed pins having a cross sectional area slightly less than a cross section of the interior of said cathode, whereby, said cathode is threadable on said pins, said pins being movable longitudinally with respect to said die, one of said pins extending through said die.

2. Apparatus for removing a portion of the coating from an indirectly heated cathode, wherein said cathode comprises a sleeve having an emitting coating on its outer surface, and comprising means for supporting said cathode, said means including two longitudinally displaced pins having a thickness enabling them to readily enter said sleeve, means for initially moving one of said pins longitudinally towards the other of said -pins and for subsequently moving both of said pins axially in a common direction, means engaging said sleeve for preventing relative motion between said sleeve and at least one of said pins, a die having an aperture therein axially disposed with respect to said pins and said sleeve, and supported against movement in any direction, said die being positioned in the path of axial movement of said sleeve.

3. Apparatus for removing a portion of the electron emitting coating from the sleeve of a cathode having open ends, comprising means for supporting said sleeve, a die having an aperture of predetermined size, and a support for said die, said sleeve being disposed coaxially with respect to said aperture in said die, means for moving said first-named means to pass said sleeve through said aperture in one direction, and means for moving said first-named means to pass said sleeve through said aperture in the opposite direction, said first-named means including two coaxially disposed and longitudinally separable pins for receiving said sleeve.

4. Apparatus for removing a portion of the electron emitting coating from the sleeve of a cathode having open ends, comprising means for supporting said sleeve, a die having an aperture of predetermined size, and a support for said die, said sleeve being disposed coaxially with respect to said aperture insaid die, means for moving said first-named means to thread said sleeve through said aperture in one direction, and means said sleeve through said aperture in the opposite direction, said first-named means including two coaxially disposed and longitudinally separable pins for receiving said sleeve, the remote ends of said pins being xed to members having surfaces lying in parallel planes transverse to the axis of said pins and serving as stop means for said sleeve.

5. Apparatus for scraping a portion of the electron emitting coating from the sleeve of a cathode having open ends, comprising a xed support and two movable supports, said fixed support including two coaxially disposed and longitudinally displaced passageways, said movable supports including two longitudinally movable members disposed within said passageways, means on each of said members movable therewith for engaging the inner walls of said sleeve to support said sleeve between said members, a die supported on said Iixed support and having an aperture in registry with said sleeve, and means for moving said rst-named means for causing said sleeve to enter said aperture, and additional means for moving said first-named means for causing said sleeve to be ejected from said aperture.

6. Apparatus for scraping a portion of the electron emitting coating from the sleeve of a cathode having open ends, comprising a xed support and movable supports, said fixed support including two coaxially disposed and longitudinal displaced passageways, said movable support including two longitudinally movable members disposed within said passageways, means on each of said members movable therewith for engaging the inner walls of said sleeve to movably support said sleeve between said members, a die supported on said fixed support and having an aperture in registry with said members, means for actuating one of said movable members for causing said sleeve to enter said aperture, including a rotatable wheel linked to one of said longitudinally movable members, and additional means for actuating the other of said movable members for causing said sleeve to be ejected from said aperture, including a tensioned spring engaging said other of said movable members.

7. Apparatus for scraping a portion of the` electron emitting coating from the sleeve of a cathode having open ends, comprising a die having an aperture therein, a fixed support for said die and movable supports for said cathode, said movable supports including two axially displaced pins having cross sections of such dimension as to permit them to enter said cathode and disposed in registry with said aperture, and being operable to axially displace said pins for threading said sleeve thereon, and means for moving said movable support to cause said pins and said sleeve to enter said aperture in said die, and to be ejected therefrom.

8. In an apparatus for scraping a portion of the electron emitting coating from the sleeve of an open ended cathode, including a die having an aperture and a xed support therefor, movable support means for said cathode comprising a pair of coaxial pins aligned with said aperture and fitting within said cathode, and means for constraining said pins to render them translatable only along their common axis, spring biasing means in registry with said aperture and one of said pinsl for causing said one of said pins to protrude through said die, and means for causing the other of said pins to move towards said one of said pins through a predetermined distance.

ARTHUR WILLIAM WARWICK GAIT. CHARLES WILLIAM TAPPING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,605,326 Bundy Nov. 2, 1926 1,623,965 Marshall Apr. 12, 1927 1,643,330 Barord Sept. 27, 1927 1,890,292 Hinsky Dec. 6, 1932 2,280,415 Larmuth Apr. 21, 1942 2,287,826 Postlewaite et al. June 30, 1942 2,293,379 Bruining Aug. 18, 1942 2,422,281 Adams June 17, 1947 

